That's impossible. Unless the previous owner used red loctite on it....
Wrenches are just going to slip off due to the wierd angle. Do you have a basic tool set with a
socket that fits? Any size ratchet wrench (even the 1/4" ones) will give you enough torque to loosen that thing up. If you don't have any tools I would really recommend buying some. This isn't the only time you'll need them. I promise.